Single-wafer optical processing of semiconductors is a powerful and versatile technique for fabrication of very-large-scale integrated (VLSI) and ultra-large-scale integrated (ULSI) electronic devices. It combines low thermal mass photon-assisted rapid wafer heating with reactive ambient semiconductor processing. Both the wafer temperature and the process environment can be quickly changed (because of short transient times) and, as a result, each fabrication step and its sub-processes can be independently optimized in order to improve the overall electrical performance of the fabricated devices.
Rapid thermal processing (RTP) of semiconductor wafers provides a capability for better wafer-to-wafer process repeatability in a single-wafer lamp-heated thermal processing reactor. Numerous silicon fabrication technologies can use RTP techniques, including thermal oxidation, nitridation, dopant diffusion, and different types of thermal anneals. Refractory metal silicide formation and chemical-vapor deposition (CVD) are other significant silicon device fabrication processes that can benefit from RTP in a single-wafer reactor. For example, CVD processes to form dielectrics (e.g., oxides and nitrides) and semiconductive materials such as amorphous silicon and polysilicon, as well as conductors (e.g., aluminum, copper, tungsten, and titanium nitride), can be performed using advanced RTP techniques for VLSI and ULSI device fabrication.
Known lamp sources for achieving these types of processes are shown in FIGS. 1 and 2. FIG. 1 shows a cold-wall system employed for rapid thermal processing of silicon that uses a single high-power low-pressure xenon arc lamp as the wafer heating energy source. The system of FIG. 1 employs a known rapid thermal processor chamber 30. The illuminator source is a single, low-pressure long xenon arc lamp 32 isolated from the reactor chamber 34 by a quartz optical window 36. A reflector 38 is used for optimal beam shaping to provide uniform wafer heating. Closed-loop wafer temperature control is performed by an optical pyrometer 40. Semiconductor wafer 42 rests on pins 43 within process chamber 34.
For further illustration, FIG. 2 illustrates another known RTP system 44 for semiconductor wafer processing. The system 44 of FIG. 2 uses two banks 46 and 48 of lamps 50 which are arranged in orthogonal or crossed directions. The lamps are placed outside the reactor chamber 52 quartz windows 54. Reflectors 56 and 58 are placed behind lamp banks 46 and 48, respectively. Quartz suscepter 62 holds semiconductor wafer 60. Semiconductor wafer 60 top and bottom surfaces face lamp banks 46 and 48. Relative power to each lamp 50 can be set and overall power can be controlled to maintain desired temperature by computer lamp controller 64. Computer lamp controller 64 receives temperature signal input from pyrometer 66. Rotary pump vacuum manifold 68 and gas manifold 70 operate to maintain process chamber 52 environment for various processes.
In the conventional RTP systems, such as those shown in FIGS. 1 and 2, equipment manufacturers have spent significant design resources to insure that the illuminator designs provide uniform wafer heating during steady-state conditions. These known systems are designed with illuminators which provide single-zone or very limited multi-zone control capability. Thus, with an increase or decrease of the power to the illuminator, the entire wafer temperature distribution is affected. As a result, there are insufficient real-time control capabilities to adjust or optimize wafer temperature uniformity during the steady-state and dynamic transient heat-up and cool-down cycles. Although known systems can provide some degree of wafer temperature uniformity under steady-state conditions, those systems do not insure that the wafer temperature will be uniform during transient heat-up and cool-down periods. As a result, the transient heat-up or cool-down process segments can result in formation of slip dislocations (at high temperatures, e.g., .gtoreq.850.degree. C.) as well as process nonuniformities. Moreover, known RTP systems do not provide any sufficient capability to adjust or optimize wafer temperature uniformity during transient conditions over extended temperature ranges. Various process parameters can influence and degrade the RTP uniformity. Known RTP systems are optimized to provide steady-state temperature uniformity at a fixed pressure such as atmospheric process pressure. Thus, a change in process pressure as well as gas flow rates can degrade the RTP uniformity.
The cross-lamp configuration of FIG. 2 attempts to provide some limited level of real-time Uniformity control for steady-state and transient heating conditions. The two-bank cross-lamp configuration of FIG. 2, however, does not provide sufficient flexibility to optimize semiconductor wafer temperature uniformity during transient heat-ups and cool-downs as well as steady-state heating conditions. One particular disadvantage of the cross-lamp configuration of FIG. 2 is that while the semiconductor wafer is circular, the cross-lamp illuminator and its associated light rays do not possess any cylindrical symmetry. Thus, changing the output power of one of the lamp banks (or a subset of the lamps in one of the lamp banks) may cause detrimental non-uniformity effects on other areas of the semiconductor wafer. Moreover, the two banks within the cross-lamp configuration are strongly coupled to one another and this further limits flexibility in attempting to adjust and optimize temperature uniformity during both steady-state and transient heating conditions. Thus, no known system provides flexible multi-zone control of wafer temperature and its uniformity during transient heat-up and cool-down as well as steady-state periods necessary for rapid thermal processing methods.
U.S. patent application Ser. No. 702,646, now U.S. Pat. No. 5,156,461, entitled "Multi-Point Pyrometry with Real-Time Surface Emissivity Compensation," by M. Moslehi, one of the present inventors describes a method and apparatus for multi-zone temperature sensing of semiconductor wafers during fabrication processing (hereinafter "M. Moslehi"). That invention describes a sensor and system that can accurately provide real-time semiconductor wafer temperature measurements at various points on the wafer. When the temperature sensor of that application is used in conjunction with the cross-lamp configuration of FIG. 2, there is some limited degree of temperature uniformity control possible during wafer heating conditions. However, because both the single arc lamp and the cross-lamp configuration do not have cylindrical symmetry, it is impossible to respond effectively to the precision multi-point temperature measurements that the invention of M. Moslehi provides.
Thus, there is a need for an improved illuminator module that provides capabilities for real-time process uniformity optimizations during the RTP fabrication processes.
There is a need for a multi-zone lamp heat source that provides wafer temperature uniformity during transient and steady-state heating conditions in a rapid thermal processing reactor.
There is a need for a multi-zone lamp module that provides cylindrical symmetry in controlling semiconductor wafer temperature and its uniformity.
Moreover, there is a need for a multi-zone illuminator heat source for use in device fabrication processes that may be effectively combined with a multi-point semiconductor wafer temperature sensor for real-time precision semiconductor wafer temperature and processing uniformity control.